the broad objective is to study phototransduction processes in the immature rod and cone photoreceptors of human infants. In normal term born infants cross-sectional studies of electroretinographic (ERG) responses to full-field stimuli will investigate phototransduction deactivation in rod and activation in cone photoreceptors. Specifically, rod isolated ERG responses to pairs of flashes will test the hypothesis that the recovery phase of the rod photoreceptor response is lower in infants than adult controls. The cone study in 4-, 10-and 18-week old infants and adult controls will test the hypothesis that the gain, or sensitivity, of cone phototransduction has a faster developmental course than does the saturated amplitude. The unexpectedly rapid development of near central, rod mediated visual sensitivity leads to the hypothesis that temporal summation will be mature at 10 degree eccentric while immature at 30 degree eccentric. A psychophysical procedure and a within subject design will assess temporal summation at 10 degree and 30 degree eccentricities in 10 week olds, 6 month olds and adult controls. The long term objective of this work, the delineation of mechanisms of retinal dysfunction and visual impairment in infantile retinal disorders, will be pursued with studies in former preterms, half with a history of non-cicatricial retinopathy of prematurity (ROP) and half with no history of ROP. ERG studies of the activation and recovery phases of the rod response, and cone responses will be conducted at post terms ages to test hypotheses about photoreceptor mechanisms. Longitudinal measures of the visual thresholds at 10 degree and 30 degree eccentricities will test the hypothesis that the near central threshold has an abnormally slow course of development in those with a history of ROP.